ACTION OF THE HEART. 365 



interval between them. In the case just alluded to, the contraction of the 

 Ventricles is stated to have been precisely synchronous with the dilatation of 

 the Auricles ; and the dilatation of the Ventricles to have been performed at 

 the same time with the contraction of the Auricles, no period of repose inter- 

 vening between the two sets of actions. It appears, however, from the con- 

 current testimony of numerous experimenters, that whilst the contraction of 

 the Ventricle immediately succeeds that of the Auricle, an interval, which is 

 usually, however, extremely brief, may elapse between the partial dilatation of 

 the Ventricles and the succeeding- systole of the Auricles. The Ventricular 

 diastole max be distinguished into two stages, of which the first immediately 

 succeeds its systole, and manifests itself in the recession of the Heart's apex 

 from the front of the chest ; whilst the second is attended with an enlargement 

 of the heart in all its dimensions, and is synchronous with the Auricular con- 

 traction. It is between these two that the interval of *repose occurs where it 

 can be observed. The following tabular view will, perhaps, make this account 

 more intelligible ; it is framed in such a manner as to commence with the 

 Auricular contraction ; but when considering the Sounds of the heart, it will 

 be necessary to commence with the Ventricular systole. 



Auricles. Ventricles. 



Contraction. 2d stage of dilatation. 



Dilatation. Contraction. Pulse. 



1st stage of dilatation. 

 Brief interval of Repose. 



Contraction. 2d stage of dilatation. 



Dilatation. Contraction. Pulse. 



483. The duration of the contraction of the Ventricles is, according to 

 Cruveilhier, double that of their Dilatation, and the same holds good of the 

 Auricles. In the Systole of the Ventricles, their surface becomes rugous; the 

 superficial veins swell ; the carnese columnae of the left ventricle are deline- 

 ated ; and the curved fibres of the conical termination of the left ventricle, 

 which alone constitutes the apex of the heart, become more manifest. During 

 their contraction, every diameter of the Ventricles is lessened ; their shorten- 

 ing is the most sensible change ; but this is owing to the vertical diameter 

 being the greatest. The lower extremity of the left ventricle, or, in other 

 words, the apex of the heart, describes a spiral movement from right to left, 

 and from behind forwards. It is to this slow, gradual, and as it were succes- 

 sive spiral contraction, that the forward movement of the apex of the heart is 

 owing, and its consequent percussion against the thoracic parietes. The 

 ventricular systole is not accompanied by a projection of the entire heart for- 

 wards (as some have maintained) ; for it is exclusively the spiral contraction, 

 which determines the approach of the apex of the heart and the thoracic 

 parietes. The Diastole of the heart, according to Cruveilhier, has the rapidity 

 and energy of an active movement, triumphing over pressure exercised upon 

 the organ, so that the hand closed upon it is opened with violence. This is 

 an observation of great importance ; but of the cause to which this active dila- 

 tation is due, no definite account can be given. It may partly be explained, 

 perhaps, by the elasticity of the tissue, interwoven with muscular fibre in the 

 substance of the heart; and this may be the cause of the first Ventricular dila- 

 tation, the second being produced by the ingress of blood occasioned by the 

 auricular systole. But the dilatation of the Auricles appears to be much 

 greater than can be accounted for by any vis a tergo (which, as will hereafter 

 appear, is extremely small in the venous system), or by the elasticity of it! 

 substance ; for it was observed in this case to be so great, that the right auricle 



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